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Assessing BC Porphyry Fertility using Zircons

Lead Researcher(s):  F. Bouzari

Project ID:  2016-032

Key Research Organization(s):  University of British Columbia - MDRU

Project Location:  North Central BC, South Central BC

Strategic Focus Area:  Minerals

Summary



This project found that the chemical and textural characteristics of zircon minerals in granite rocks that typically host porphyry copper deposits can help identify rocks that formed under 'copper-friendly' (fertile) conditions.

Exploring British Columbia’s Porphyry Copper Deposits using Zircon, Apatite and Titanite Webinar – October 2020

Geoscience BC co-hosted an online webinar with MDRU – Mineral Deposit Research Unit on October 21, 2020 to discuss a series of research projects that show the potential to identify buried porphyry deposits from till or bedrock samples near the surface in British Columbia.

The Need

Finding additional copper deposits is important to BC’s economy and to meeting forecast increases in global demand.

Zircon is a mineral often found in rocks that host copper porphyry deposits. Zircons are some of the oldest and toughest minerals found on earth. Often referred to as ‘time capsules’ these minerals lock in information about the conditions that existed during their formation and are tough enough to survive high temperatures (such as within a magma) and in surface sediments, carried for miles by rivers and rain.

The trace elements found in zircon mineral grains can provide information on the magma before it solidified into rock, as well as the age of the rock. Internal textures and zoning within the zircon grains can also give clues to the environment of the rock’s formation and ore-forming processes, thereby helping mineral explorers determine if a rock formed under potentially ‘copper-friendly’ conditions.

Project Goals

This project fits under Geoscience BC’s Strategic Objective of Advancing Science & Innovative Geoscience Technologies and our goal to:

  • Increase research and development of innovative exploration and mining methods, tools, approaches and geoscience technologies.

Specifically, the goal of this project was to develop an exploration toolkit to evaluate porphyry fertility in BC plutons by:

  • Determining the mineralogical features that characterize and distinguish fertile porphyry intrusions;
  • Assessing the features and geochemistry of the common accessory mineral zircon that can indicate fertility; and
  • Documenting fertility evidence over time and space within an evolving composite zoned pluton.
  • Assessing the utilization of rapid, automatic mineralogical characterization tools such as mineral liberation analysis.

These objectives were accomplished using field, mineralogical and geochemical techniques on fertile and barren plutons.

Project Benefits

Recent studies show that zircon provides a useful tool to evaluate a pluton’s fertility or ability to generate porphyry copper deposits. This study can help to determine if a rock formed under potentially ‘copper-friendly’ conditions.

Survey Area

Samples were collected from batholiths in BC’s South Central and North Central Regions that host porphyry copper deposits, including:

  • Takomkane Batholith, host to the Woodjam porphyry district
  • Guichon Creek Batholith, host to Highland Valley Copper mine
  • Granite Mountain Batholith, host to the Gibraltar mine
  • Toodoggone Batholith, host to the Kemess mine.

What Was Found

The researchers analyzed 1,021 zircon grains from 42 rock samples. They found that zircon mineral grains from porphyry-fertile batholiths in BC have characteristics that record distinct chemical and physical properties and indicate increased potential to host porphyry copper deposits.

The researchers identified key features of zircon that indicate porphyry-fertile plutons in BC. They contain zircons with:

  • Oscillatory zoning, particularly those with regular zoning patterns.
  • Evidence of simple crystal fractionation, with values on a Yb/Gd versus Th/U curve, which suggests fractionation without crustal contamination.
  • Titanium in zircon model temperatures below 750°C.
  • Europium anomaly values typically equal to or above 0.35 suggest a high oxidation state and high magmatic water content.
  • Europium anomaly values that are not dependent on hafnium concentration or Yb/Gd values. This suggests that magmatic water content and oxidation state were high and remained high during much of the magma crystallization.

Deliverables